This invention relates to progressing-cavity-type positive displacement helical pumps for handling fluid, semi-fluid and comminuted material, such as the progressing cavity helical pump of my U.S. Pat. No. 3,512,904. More particularly, the invention relates to an improved means for flexibly coupling the orbiting rotor for the pump to the rotary drive therefor.
Progressing-cavity-type positive displacement rotary devices of the general class that includes the device disclosed in my U.S. Pat. No. 3,512,904 (hereinafter referred to as "Allen" devices or pumps) have a rotor with an exterior helical surface that engages the surrounding interior helical surface of the stator, the rotor surface having one more thread than the stator surface and a lead twice that of the stator surface. Thus, the stator surface and rotor surface define therebetween sealed pumping cavities that are axially advanced as the rotor rotates and at the same time orbits in the same direction at two or more times the rate of its rotation. For a more complete description of pumps of this type, reference is made to my aforesaid U.S. Pat. No. 3,512,904.
This class of rotary helical devices differs from the well known Moineau type device as disclosed, for example, in U.S. Pat. No. 1,892,217. In the Moineau-type device the helical rotor orbits in the reverse direction relative to its rotation and the helical stator surface has one thread more than the helical rotor.
The coupling between the Moineau rotor and drive shaft must utilize a universal connection to accommodate the orbital motion of the rotor, the orbital speed being equal to the speed of rotation. Various types of universal connections or couplings have been utilized including conventional universal joints, long flexible tubes etc. Since the rotor has a cork screw shape, it is not feasible to locate the flexible coupling within the rotor and normally coupling devices of relatively long length are used such as those disclosed in U.S. Pat. Nos. 2,512,764; 2,545,626; 2,737,119; 2,739,650 and 2,924,180.
Another technique that is used in connection with Moineau-type pumps is the provision of a flexible mounting for the helical stator as disclosed in U.S. Pat. Nos. 2,826,152; 2,862,454 and 3,667,692. This arrangement permits the rotor to be rigidly coupled to the rotary drive shaft and also avoids the use of long-length universal coupling mechanisms which greatly add to the overall size of the device. The flexible stator design, however, results in the stator, which is usually formed of elastomeric material, being vulnerable to malfunction under excessive pressure since it is able to deflect in an axial direction. Also, this type of design results in the generation of considerable heat due to the flexing of the elastomeric material and excessive heat can greatly reduce the effective life of the stator. While this flexible mounting technique may be used in connection with Allen-type devices, it would be vulnerable to the same disadvantages.
One particular application for Allen pumps is in the pumping of sewage in pressure sewage systems. In these systems, it is desirable that a grinding mechanism be utilized to comminute any solid material before it enters the pumping section. Accordingly, it is desirable to use the same rotary drive shaft for both the grinder and the pump. A typical pumping and comminuting device for use in a pressure sewage system is disclosed in U.S. Pat. No. 3,667,692. This type of device has a rotary cutter blade or grinding wheel mounted on the lower end of a vertical drive shaft below the surface of the sewage in a reservoir. Mounted on the rotor shaft immediately above the grinder head is a rotary pump unit which may be a centrifugal type pump or in the case of U.S. Pat. No. 3,667,692, a Moineau-type positive displacement pump.
In the case of the Moineau pump, since the drive shaft must extend through and below the rotor, the rotor is fixed to the shaft and the elastomeric stator is flexibly mounted with a flexible bellows type arrangement. In this particular application for a Moineau pump, the flexible stator arrangement must be utilized rather than a universal coupling between the drive shaft and the rotor because the shaft must extend through the rotor to the grinding blade unit. The flexible mounting for the stator, however, results in the disadvantages described above.
The shaft-rotor universal coupling arrangement of the present invention has many potential uses, however, it has particular utility in connection with the pressure sewage systems wherein it is combined with a comminutor.